Many species of bacteria can exchange chemical signals to help them monitor their population densities, a phenomenon referred to as quorum sensing. Vibrio cholerae, the causative agent of the epidemic diarrheal disease cholera, has been shown to have dual quorum sensing systems, one of which is similar to that of V. harveyi. Preliminary results show that quorum sensing is involved in biofilm formation and pathogenesis in V. cholerae. However, quorum-regulated genes remain largely unidentified in V. cholerae. The goal of this research is to identify quorum sensing regulated genes in V. cholerae by using whole genome microarray expression analysis. The first aim of these experiments is to identify a novel AI synthase and components required for AI signal transduction in V. cholerae by genetic screening. The second aim is to identify quorum-regulated genes using microarray analysis. RNA isolated from wild-type and autoinducer synthase mutants grown under different conditions will be subjected to microarray analysis. The next aim is to characterize these quorum-regulated genes and understand how quorum sensing affects V. cholerae pathogenesis. The final aim is to study the expression patterns of quorum-regulated genes in various V. cholerae biotypes to determine if there is any correlation between the prevalence of quorum sensing systems and the emergence of epidemic strains.